Gastroesophageal reflux is a condition in which gastric acid refluxes, or flows in the direction opposite to the normal flow, from the stomach into the esophagus. Frequent reflux episodes may result in a potentially severe problem known as gastroesophageal reflux disease (GERD). GERD is the most common cause of dyspepsia or heartburn. GERD affects approximately 75 million adults in the United States on at least an intermittent basis, and approximately 13 million adults on a daily basis. As a common cause of chest pain, GERD frequently mimics the symptoms of a myocardial infarction or severe angina pectoris, which are signs of severe coronary artery disease. Because their treatments and outcomes are different, distinguishing between GERD and coronary artery disease is of paramount diagnostic importance to the patient and physician. Complications of GERD may include esophageal erosion, esophageal ulcer, and esophageal stricture. Prolonged exposure of esophageal mucosa to acid often leads to a precancerous condition known as Barrett's esophagus.
Efforts have been made to define and report as reflux rapid changes of intraesophageal pH, even while the pH remains within the normal esophageal pH range of 4 to 7. Such pH changes, however, can be difficult to prove to be caused by true gastroesophageal reflux, and in some instances may not be caused by reflux. The primary and most reliable method of objectively diagnosing GERD is 24-hour measurement of pH within the lower esophagus. A pH reading corresponds to the negative logarithm of the hydrogen ion concentration, and is represented on a scale of 0 to 14, with pH values above 7 corresponding to basic conditions, and pH values below 7 corresponding to acidic conditions. As a general rule, when gastric acid enters the esophagus from the stomach, the intraesophageal pH drops below 4. An epoch of one second or more during which the intraesophageal pH falls below 4 is generally considered a reflux event.
Sensing electrodes have been used to measure pH. Electrodes are generally of three types, counter electrodes, indicator electrodes and reference electrodes. A counter electrode acts as a sink for a current path. An indicator electrode (also known as a working or measurement electrode) selectively measures a specific chemical species, such as an ion. A reference electrode generally serves as an electrical reference point in an electrochemical device against which electrical potentials are measured and controlled. When electrical potentials are measured by an indicator electrode, the method is termed potentiometry.